There have been no signs of the boy or any eyewitness reports of him, according to police.

Bears are sometimes spotted in the Hokkaido mountains and a local hunter has been added to the search party after fresh tracks were found in the area where he vanished from, Jiji news agency said.

The boy's mysterious disappearance has captured national attention, with many praying for his safe return, while others have bitterly criticized the parents, triggering a debate over whether their treatment of the boy was discipline or child abuse.

JIJI PRESS via Getty ImagesThe Japanese military has joined the search for missing Yamato Tanooka

Police said the parents said they made the boy get out of the car as "discipline," after changing their earlier story that he disappeared while picking wild vegetables.

The father said the boy was gone when he returned to the site several minutes later, police said.

The parents reportedly told police that they had punished the boy for throwing rocks at people and cars while playing at a river earlier in the day.

Police said they are considering whether the parents should be charged with child abandonment.

The boy’s father Takayuki Tanooka told television reporters: “We have done an unforgiveable thing to our child and we have caused a lot of trouble for everyone. I just hope he is safe.”

"Making children obey by giving them fear or pain is bad parenting," Naoki Ogi, a professor of education at Hosei University, said in his blog. "It's abuse."